Big yield recipe includes lots of heavy kernels

No one in their right mind last June would have guessed farmers would harvest near-record yields in 2009. Not even someone with a crystal ball could have come up with that prediction.

Yet what was unthinkable nine months ago is now history. The proof is still sitting in grain bins on farms and in elevator terminals. Inquiring minds want to know: Where did all that corn come from?

“Not all factors that affect corn yields are negative,” says Bob Nielsen. The Nebraska native is an Extension corn specialist at Purdue University. “There are positive factors that impact yield, too. Some of them came into play during 2009.”

Key Points

• Few aborted kernels and heavy kernels contribute to big yields.

• Most kernel abortion happens in blister to early milk stages.

• Cool summers usually mean longer grain-fill periods.

2 key factors

Superb grain fill during pollination depends upon putting as many kernels on each ear as possible, and making those kernels heavy. There were exceptions, but by and large, there tended to be more kernels per ear and heavier kernels in most situations in ’09, Nielsen says.

Harvesting more kernels per ear stems primarily from less kernel abortion. A longer grain-fill period tends to be desirable, he notes. It happened in ’09 as record cool July weather throttled back pollination and grain fill.

“It’s a balancing act,” Nielsen explains. “Cool weather makes for a longer grain-fill period, and that’s a plus.

“On the other hand, when it’s warmer, you get more dry matter produced per day. That’s also desirable,” he notes. “But in cases of cool summers, the longer grain-fill period seems to win out.”

What’s not a plus is stress at pollination. For example, drought stress commonly delays silk emergence and hastens onset of pollen shed. Sometimes the two do not coincide. That’s when poor kernel set can result.

Instead, cool temperatures and ample soil moisture favor prolonged, rapid silk elongation.

Check kernel set

“You’ve got to get out of your truck to assess kernel set,” Nielsen quips. “You can’t do it from the edge of the field. If you took time to walk fields last year, you likely found good kernel set.”

What you don’t want at that stage is kernel abortion, he notes. Stress even at the blister stage often leads to kernel abortion. Ears decide the conditions won’t allow them to fill as many kernels.

According to Dave Nanda, a plant breeder and crops consultant: “The goal of the plant is to make as many babies as possible. The plant wants progeny. When outside stresses tell it that it can’t handle as many progeny as it thought, it cuts back, hoping to produce as many good seeds as possible.”

Any kind of stress at the blister stage can lead to kernel abortion, Nielsen observes. Drought stress is one of the most common. Other stresses that can cause kernel abortion include severe nutrient deficiencies, severe leaf disease symptoms, leaf loss following hail and severe tunneling by European corn borers.

A pair of environmental factors also can cause abortion, Nielsen adds. Excessively warm nights during or shortly after pollination lead to more aborted kernels. Likewise, consecutive cloudy days during or shortly after pollination trigger it. Neither of those conditions were a factor in ’09.

“Once you get to the dough stage, it’s harder for the ear to abort kernels,” Nielsen explains. “Kernels may wind up small if conditions go sour, but they won’t be completely absent.”

Big kernels

The more starch that goes into kernels, the heavier the kernels. The heavier each kernel becomes, the better the odds for higher yields, Nielsen says.

The same factors that can abort kernels at the blister stage can affect the weight of kernels once corn reaches the early dough stage, he suggests. Besides the factors mentioned already, stalk rots and an early killing frost come into play, especially if the crop was planted late. Those two factors trimmed back yields in certain sections of corn-growing states last fall.

Otherwise, the plant creates dry matter as long as it can, and kernels grow heavy, Nielsen says. Without photosynthetic stress, the process continues. Those are the situations where fields are set up for big yields, he contends.

Building the corn factory

What happened in 2009 makes more sense if you think of corn plants as factories, Bob Nielsen says. “We’re constructing a factory every year,” the corn specialist insists.

“Every decision that you make influences the size and scope of that factory, from the hybrid you select to the seeding rate and row width you choose,” he says.

This factory turns sunlight into food. Building an adequate canopy to intercept sunlight, and then maintaining that canopy throughout grain fill, produces top yields, he adds.

Other factors farmers control that help determine the size of the factory include soil fertility, weed control, planting date, foliar fungicides and irrigation.

Some factors affecting health of the canopy aren’t in the farmer’s control, including soil moisture and temperature patterns.

“Your job is to keep the factory healthy,” Nielsen concludes. When that happens, 2009-like yields are possible.

Understand how test weight factors in

Whenever Bob Nielsen speaks at winter meetings and says heavier kernels contributed to higher yields for 2009, hands shoot up almost immediately. Many people reported lower test weights. How could kernels be heavier if test weights were lower?

Nielsen emphasizes that the test weight concept is very difficult to explain, and even harder to understand. “The truth is that test weight and how heavy kernels are just isn’t the same thing,” he explains.

Test weight is the amount of grain that fits into a standard measure, he notes. Size and shape of kernel, not just weight, influence how many kernels fit into the cup. Low test weight doesn’t always indicate poor quality, he adds.

“It depends on what caused low test weight,” Nielsen relates. “For example, if it’s dry and you get low test weight, protein was likely laid down first in the kernel, then starch. When it came time for starch, there weren’t enough resources to go around.

“As far as feeding value, protein content may actually be slightly higher than normal because there’s a higher percentage of protein in each kernel,” Nielsen says.

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STARVED IN GOOD YEAR: A few areas of the Corn Belt didn’t participate in 2009’s yield bonanza. These ears show excessive kernel abortion near the tip, caused by lack of rain on sandy ground.

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FANCY FACTORY: Here’s a corn factory in top shape, hard at work capturing sunlight on a summer day.

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EAR OF PLENTY: Properly pollinated ears filled with plump kernels add up to a big corn crop.

This article published in the March, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.